Hydrocracking of hydrocarbon feedstocks is often used to convert lower value hydrocarbon fractions into higher value products, such as conversion of vacuum gas oil (VGO) feedstocks to various fuels and lubricants. Typical hydrocracking reaction schemes can include an initial hydrotreatment step, a hydrocracking step, and a post hydrotreatment step, such as dewaxing or hydrofinishing. After these steps, the effluent can be fractionated to separate out a desired diesel fuel and/or lubricant oil base oil.
A process train for hydrocracking a feedstock can be designed to emphasize the production of fuels or the production of lubricant base oils. During fuels hydrocracking, typically the goal of the hydrocracking is to cause conversion of higher boiling point molecules to molecules boiling in a desired range, such as the diesel boiling range, kerosene boiling range, and/or naphtha boiling range. Many types of fuels hydrocracking processes also generate a bottoms component from hydrocracking that potentially can be used as a lubricant base oil. However, the lubricant base oil is produced in a lesser amount, and often is recycled and/or hydrocracked again to increase the fuels yield. In hydrocracking for forming a lubricant base oil the goal of the hydrocracking is typically to remove contaminants and/or provide viscosity index uplift for the feed. This results in some feed conversion, however, so that a hydrocracking process for generating a lubricant base oil typically produces a lesser amount of fractions that boil in the diesel boiling range, kerosene boiling range, and/or naphtha boiling range. Due to the difference in the desired goals, the overall process conditions during fuels hydrocracking of a given feedstock typically differ from the overall process conditions during hydrocracking for lubricant base oil production on a similar type of feedstock.
U.S. Pat. No. 7,261,805 describes a method for dewaxing and cracking of hydrocarbon streams. A feedstock with an end boiling point exceeding 650° F. (343° C.) is contacted with a hydrocracking catalyst and an isomerization dewaxing catalyst to produce an upgraded product with a reduced wax content. The feedstock is described as contacting the hydrocracking catalyst first, but it is noted that the order of the steps can be changed without a significant decrease in yield.
U.S. Patent Application Publication 2012/0080357 describes a method for hydrocracking a feedstream to produce a converted fraction that includes a high distillate yield and improved properties and an unconverted fraction that includes a lubricant base oil fraction with improved properties. The hydrocracking can be a two-stage hydrocracking system that includes a USY catalyst and a ZSM-48 catalyst.
U.S. Pat. No. 8,303,804 describes a method for producing a jet fuel, such as by hydrotreatment and dewaxing of a kerosene feedstock. The dewaxing can be performed using a ZSM-48 catalyst.